A surface reducing reflection and transmitting or absorbing light well has direct relationship with efficiency of optical device in solar photovoltaic generation as well as various displays, road signs, and various optical devices, so is an issue recently. In particular, currently developed low reflective surfaces or low reflective coating techniques are poor durability against contaminations, so has a difficulty in commercialization due to deterioration of its low reflection property and difficulty in management with the lapse of time.
Low reflective surface found in nature includes eyes of nocturnal insects. These eyes have a special micro-nano scale structure and many researches have obtained anti-reflecting effect by applying the structure. These regular array of protuberances enables them to live with minimum light even in night by reducing light reflectance and increasing transmission [S. J. Wilson & M. C. Nutley, “The Optical Properties of ‘Moth Eye’ Antireflection Surfaces,” Optica Acta: International Journal of Optics, Volume 29, issue 7, 1982].
A lot of methods to conventionally prepare the regular array of protuberances have been suggested by other researchers. Representative techniques include E-beam evaporator, CVD, RF sputtering, plasma etching, RIE, sol-gel, hydrothermal method, and so forth. In 2012, it has been reported to develop a self-cleaning Si surface using RIE and nano imprinting technology, in which reflectance is significantly lowered and durability is enhanced [journal ACS Nano: “Nanotextured Silica Surfaces with Robust Super-Hydrophobicity and Omnidirectional Broadband Super-Transmissivity, 2012, K. C. Park, H. Choi etc]. However, this method has some demerits such as complicated preparation process and significantly high cost because it is required to prepare a mask previously and the process is composed of several steps. As another study, there has been an attempt for application to a photovoltaic cell to fabricate a pyramid structure on a silicone surface using wet etching to be a relatively cheap and simple method, and since HF is utilized as an etchant, this process has drawbacks including risks in process and high cost for safety equipment [Georgia Institute of Technology, 2009, John Toon, Self-cleaning, low-reflectivity treatment boosts efficiency for photovoltaic cells, not published].
Accordingly, to overcome these problems, the present invention suggests a method to reduce a surface reflectance with a simple, relatively cheap, and eco-friendly process and the surface structure using the same.